Effects of Sewage Effluents on Water Quality in Tropical Streams
- Débora Figueroa-Nieves *a,
- William H. McDowella,
- Jody D. Pottera,
- Gustavo Martínezb and
- Jorge R. Ortiz-Zayasc
- a Dep. of Natural Resources and the Environment, Univ. of New Hampshire, Durham, NH 03824
b Crops and Agro-Environmental Science Dep., College of Agricultural Sciences, Univ. of Puerto Rico-Mayagüez Campus, 1193 Guayacán St. San Juan, PR 00926
c Institute for Tropical Ecosystem Studies, Univ. of Puerto Rico-Río Piedras Campus, PO Box 363682 San Juan, PR 00936
Increased urbanization in many tropical regions has led to an increase in centralized treatment of sewage effluents. Research regarding the effects of these wastewater treatment plants (WWTPs) on the ecology of tropical streams is sparse, so we examined the effects of WWTPs on stream water quality on the Caribbean island of Puerto Rico. Nutrient concentrations, discharge, dissolved oxygen (DO), biochemical oxygen demand (CBOD5), and specific UV absorbance (SUVA) at 254 nm were measured upstream from the WWTP effluent, at the WWTP effluent, and below the WWTP effluent. All parameters measured (except DO) were significantly affected by discharge of WWTP effluent to the stream. The values of SUVA at 254 nm were typically lower (<2.5 m−1 mg L−1) in WWTP effluents than those measured upstream of the WWTP, suggesting that WWTP effluents are contributing labile carbon fractions to receiving streams, thus changing the chemical composition of dissolved organic carbon in downstream reaches. Effluents from WWTP contributed on average 24% to the stream flow at our tropical streams. More than 40% of the nutrient loads in receiving streams came from WWTP effluents, with the effects on NO3−–N and PO4−–P loads being the greatest. The effect of WWTPs on nutrient loads was significantly larger than the effect of flow due to the elevated nutrient concentrations in treated effluents. Our results demonstrate that inputs from WWTPs to streams contribute substantially to changes in water quality, potentially affecting downstream ecosystems. Our findings highlight the need to establish nutrient criteria for tropical streams to minimize degradation of downstream water quality of the receiving streams.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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